Check out the Gardening in Shade and Woodland Wildflower forums. There are many flowers, bushes, etc. that will grow in northern Wisconsin. Bushes such as Azaleas, hardy rhododendrons, serviceberry; woodland wildflowers like trillium, bloodroot, spring beauty, wood anemone; perennials like astilbe, goatsbeard, monkshood, epimediums, and don't forget the spring bulbs like tulips, crocus, scilla, snowdrops, etc. These latter flower before the trees are leafed out and you can plant hostas nearby to cover the dying foliage during late spring.

Hi David. I saw your post on the GardenWeb's Northern Gardening forum. You mentioned Green Bay?? That's where I'm from and I moved to southwest Florida just this past October. I am now trying to figure out how to garden here in the tropics. I guess now I won't have to worry about giving my roses winter protection any more! :-)